Where possible, crane vessels are used to carry their load to an offshore site. The crane is used to lift the load off the deck of the vessel and slew it round to the required position for installation. In some cases, this procedure is not possible, for example, if slewing over the side is restricted by lack of stabilization or if the load is so heavy that it has to be handled by two or more cranes. Heavy lift offshore cranes are commonly able to handle far heavier loads if used in a fixed working position than when they are used in slewing mode. In a fixed working position, the crane can be provided with additional strengthening, eg, a back stay between the boom tip and the deck, to further increase its lifting capacity. In such cases, however, it is necessary to have a cargo barge from which to pick up the load. This conventional procedure is illustrated in FIGS. 1A to 1C of the accompanying drawings. The procedure has the disadvantage of requiring a separate barge, and workability is restricted because of relative movements between the cargo barge and crane vessel.